1 // Copyright 2010 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // The routines exported by this module are subtle. If you use them, even if 6 // you get the code right, it will depend on careful reasoning about atomicity 7 // and memory ordering; it will be less readable, and harder to maintain. If 8 // you plan to use these routines, you should have a good reason, such as solid 9 // evidence that performance would otherwise suffer, or there being no 10 // alternative. You should assume only properties explicitly guaranteed by the 11 // specifications in this file. You are almost certainly _not_ writing code 12 // just for the x86; if you assume x86 semantics, x86 hardware bugs and 13 // implementations on other archtectures will cause your code to break. If you 14 // do not know what you are doing, avoid these routines, and use a Mutex. 15 // 16 // It is incorrect to make direct assignments to/from an atomic variable. 17 // You should use one of the Load or Store routines. The NoBarrier 18 // versions are provided when no barriers are needed: 19 // NoBarrier_Store() 20 // NoBarrier_Load() 21 // Although there are currently no compiler enforcement, you are encouraged 22 // to use these. 23 // 24 25 #ifndef V8_BASE_ATOMICOPS_H_ 26 #define V8_BASE_ATOMICOPS_H_ 27 28 #include <stdint.h> 29 #include "src/base/build_config.h" 30 31 #if defined(_WIN32) && defined(V8_HOST_ARCH_64_BIT) 32 // windows.h #defines this (only on x64). This causes problems because the 33 // public API also uses MemoryBarrier at the public name for this fence. So, on 34 // X64, undef it, and call its documented 35 // (http://msdn.microsoft.com/en-us/library/windows/desktop/ms684208.aspx) 36 // implementation directly. 37 #undef MemoryBarrier 38 #endif 39 40 namespace v8 { 41 namespace base { 42 43 typedef char Atomic8; 44 typedef int32_t Atomic32; 45 #if defined(__native_client__) 46 typedef int64_t Atomic64; 47 #elif defined(V8_HOST_ARCH_64_BIT) 48 // We need to be able to go between Atomic64 and AtomicWord implicitly. This 49 // means Atomic64 and AtomicWord should be the same type on 64-bit. 50 #if defined(__ILP32__) 51 typedef int64_t Atomic64; 52 #else 53 typedef intptr_t Atomic64; 54 #endif // defined(V8_HOST_ARCH_64_BIT) 55 #endif // defined(__native_client__) 56 57 // Use AtomicWord for a machine-sized pointer. It will use the Atomic32 or 58 // Atomic64 routines below, depending on your architecture. 59 typedef intptr_t AtomicWord; 60 61 // Atomically execute: 62 // result = *ptr; 63 // if (*ptr == old_value) 64 // *ptr = new_value; 65 // return result; 66 // 67 // I.e., replace "*ptr" with "new_value" if "*ptr" used to be "old_value". 68 // Always return the old value of "*ptr" 69 // 70 // This routine implies no memory barriers. 71 Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr, 72 Atomic32 old_value, 73 Atomic32 new_value); 74 75 // Atomically store new_value into *ptr, returning the previous value held in 76 // *ptr. This routine implies no memory barriers. 77 Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, Atomic32 new_value); 78 79 // Atomically increment *ptr by "increment". Returns the new value of 80 // *ptr with the increment applied. This routine implies no memory barriers. 81 Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, Atomic32 increment); 82 83 Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr, 84 Atomic32 increment); 85 86 // These following lower-level operations are typically useful only to people 87 // implementing higher-level synchronization operations like spinlocks, 88 // mutexes, and condition-variables. They combine CompareAndSwap(), a load, or 89 // a store with appropriate memory-ordering instructions. "Acquire" operations 90 // ensure that no later memory access can be reordered ahead of the operation. 91 // "Release" operations ensure that no previous memory access can be reordered 92 // after the operation. "Barrier" operations have both "Acquire" and "Release" 93 // semantics. A MemoryBarrier() has "Barrier" semantics, but does no memory 94 // access. 95 Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr, 96 Atomic32 old_value, 97 Atomic32 new_value); 98 Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr, 99 Atomic32 old_value, 100 Atomic32 new_value); 101 102 void MemoryBarrier(); 103 void NoBarrier_Store(volatile Atomic8* ptr, Atomic8 value); 104 void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value); 105 void Acquire_Store(volatile Atomic32* ptr, Atomic32 value); 106 void Release_Store(volatile Atomic32* ptr, Atomic32 value); 107 108 Atomic8 NoBarrier_Load(volatile const Atomic8* ptr); 109 Atomic32 NoBarrier_Load(volatile const Atomic32* ptr); 110 Atomic32 Acquire_Load(volatile const Atomic32* ptr); 111 Atomic32 Release_Load(volatile const Atomic32* ptr); 112 113 // 64-bit atomic operations (only available on 64-bit processors). 114 #ifdef V8_HOST_ARCH_64_BIT 115 Atomic64 NoBarrier_CompareAndSwap(volatile Atomic64* ptr, 116 Atomic64 old_value, 117 Atomic64 new_value); 118 Atomic64 NoBarrier_AtomicExchange(volatile Atomic64* ptr, Atomic64 new_value); 119 Atomic64 NoBarrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment); 120 Atomic64 Barrier_AtomicIncrement(volatile Atomic64* ptr, Atomic64 increment); 121 122 Atomic64 Acquire_CompareAndSwap(volatile Atomic64* ptr, 123 Atomic64 old_value, 124 Atomic64 new_value); 125 Atomic64 Release_CompareAndSwap(volatile Atomic64* ptr, 126 Atomic64 old_value, 127 Atomic64 new_value); 128 void NoBarrier_Store(volatile Atomic64* ptr, Atomic64 value); 129 void Acquire_Store(volatile Atomic64* ptr, Atomic64 value); 130 void Release_Store(volatile Atomic64* ptr, Atomic64 value); 131 Atomic64 NoBarrier_Load(volatile const Atomic64* ptr); 132 Atomic64 Acquire_Load(volatile const Atomic64* ptr); 133 Atomic64 Release_Load(volatile const Atomic64* ptr); 134 #endif // V8_HOST_ARCH_64_BIT 135 136 } // namespace base 137 } // namespace v8 138 139 // Include our platform specific implementation. 140 #if defined(THREAD_SANITIZER) 141 #include "src/base/atomicops_internals_tsan.h" 142 #elif defined(_MSC_VER) && (V8_HOST_ARCH_IA32 || V8_HOST_ARCH_X64) 143 #include "src/base/atomicops_internals_x86_msvc.h" 144 #elif defined(__APPLE__) 145 #include "src/base/atomicops_internals_mac.h" 146 #elif defined(__native_client__) 147 #include "src/base/atomicops_internals_portable.h" 148 #elif defined(__GNUC__) && V8_HOST_ARCH_ARM64 149 #include "src/base/atomicops_internals_arm64_gcc.h" 150 #elif defined(__GNUC__) && V8_HOST_ARCH_ARM 151 #include "src/base/atomicops_internals_arm_gcc.h" 152 #elif defined(__GNUC__) && V8_HOST_ARCH_PPC 153 #include "src/base/atomicops_internals_ppc_gcc.h" 154 #elif defined(__GNUC__) && (V8_HOST_ARCH_IA32 || V8_HOST_ARCH_X64) 155 #include "src/base/atomicops_internals_x86_gcc.h" 156 #elif defined(__GNUC__) && V8_HOST_ARCH_MIPS 157 #include "src/base/atomicops_internals_mips_gcc.h" 158 #elif defined(__GNUC__) && V8_HOST_ARCH_MIPS64 159 #include "src/base/atomicops_internals_mips64_gcc.h" 160 #else 161 #error "Atomic operations are not supported on your platform" 162 #endif 163 164 // On some platforms we need additional declarations to make 165 // AtomicWord compatible with our other Atomic* types. 166 #if defined(__APPLE__) || defined(__OpenBSD__) || defined(V8_OS_AIX) 167 #include "src/base/atomicops_internals_atomicword_compat.h" 168 #endif 169 170 #endif // V8_BASE_ATOMICOPS_H_ 171
